Along with the development of high-frequency electronic apparatuses, there have been strong demands for capacitors serving as one kind of electronic apparatuses that have a superior impedance characteristic in a high-frequency region in comparison with the conventional capacitor, and in order to address these demands, various kinds of solid electrolytic capacitors in which a conductive polymer having a high electric conductivity is used as a solid electrolyte have been examined.
Moreover, in recent years, with respect to solid electrolytic capacitors to be used around a CPU of a personal computer, there have been strong demands for miniaturization of the electrolytic capacitors with a large capacitance, and there have also been demands for them to have a low equivalent series resistance (ESR) so as to respond to high frequencies and a low equivalent series inductance (ESL) that is superior in removing noise as well as in transient response.
FIG. 9 is a perspective view of conventional solid electrolytic capacitor 501 described in Patent Literature 1. FIG. 10 is a plan view of capacitor element 21 of solid electrolytic capacitor 501. Capacitor element 21 includes an electrode foil that is an anode made of a valve metal foil, such as an aluminum foil, and a dielectric oxide layer formed on a surface of the electrode foil. The surface of the electrode foil is roughened. The electrode foil is separated into anode portion 23 and a cathode formation portion by insulating resist 22 formed on the dielectric oxide layer. Capacitor element 21 further includes a solid electrolyte layer made of a conductive polymer formed on the dielectric oxide layer on the cathode formation portion of the electrode foil, and a cathode layer formed on the solid electrolyte layer. The cathode layer includes a carbon layer formed on the solid electrolyte layer, and a silver paste layer formed on the carbon layer. The solid electrolyte layer and the cathode layer constitute cathode portion 24. The electrode foil has a rectangular shape extending in a longitudinal direction, and capacitor element 21 has a flat-plate shape. Anode portion 23 and cathode portion 24 are arranged in the longitudinal direction while resist 22 is provided between portions 23 and 24.
Anode common terminal 25 is connected to anode portion 23 of capacitor element 21. A plurality of capacitor elements 21 are stacked on anode common terminal 25, and anode portions 23 of capacitor elements 21 are joined to one another by a joining method, such as laser welding.
Cathode common terminal 26 is connected to cathode portion 24 of capacitor element 21. Bent portions 26A are formed by bending two sides of an element mounting portion of cathode common terminal 26 upward. The element mounting portion of cathode common terminal 26 and cathode portions 24 of capacitor elements 21 are electrically connected to each other by a conductive adhesive, and cathode portions 24 of capacitor elements 21 are also electrically connected to one another by a conductive adhesive. Bent portions 26A and cathode portion 24 are joined by conductive adhesive 27 so as to be electrically connected to each other.
Capacitor elements 21 are unitarily covered with insulating package resin 28, with one portion of each of anode common terminal 25 and cathode common terminal 26 being exposed to an outer surface. Portions of anode common terminal 25 and cathode common terminal 26 which extend outside from package resin 28 are bent toward the bottom surface along package resin 28 so that surface mounting solid electrolytic capacitor 501 having the anode terminal portion and the cathode terminal portion formed on the bottom surface portion is configured.
In conventional solid electrolytic capacitor 501, in an attempt to increase its capacitance by enlarging the surface area per unit area of the electrode foil, the surface of the electrode foil made of an aluminum foil of capacitor element 21 is roughened by an etching process. From the viewpoints of the etching technique and the mechanical strength of the aluminum foil, there is a limitation in further increasing of the surface area by the etching process, and it is difficult to increase the capacitance beyond this limitation.